On Jun 18, 2:48 pm, "Michael Tobis" <[EMAIL PROTECTED]> wrote:
> Interesting that ref 15 (Forest, Stone & Sokolov, GRL33 L01705) is out
> of MIT, home of Dick "what-me-worry?" Lindzen.
>
> They have anticipated James' response, I expect:
>
> "When using unifrom priors on all parameters, these new results are
> summarized by the 90% confidence bounds of 2.1 to 8.9 K for climate
> sensitivity... We note that the upper bound for the climate
> sensitivity is sensitive to our choice fo prior, which was truncated
> at 10 K. WHen an expert prior for S is used [Forest et al 2002
> (Science 295 113-117)] the 90% confidence intervals are 1.9 to 4.7
> K... for S... "
>
> All this amounts to is that the dataset in question is insufficient to
> constrain S very well. If you really want to know S, you use
> allavailable information, which can be embodied in an expert prior. A
> non-truncated prior is mathematically unworkable, and a truncated
> prior just amounts to a particularly foolish choice of prior. The high
> end you get back out (in this case 8.9 K) is pretty much the same as
> the high end you put in (10 K) and tells you nothing.
>
> Note the following in the concluding paragraph
>
> "Despite their uncertainties, the paleoclimate results provide data
> not directly included in the present framework... and this supports
> using a prior influenced by such results."
>
> This is clear enough to the peer audience, but that group is very
> narrow, and it seems likely that Matthews and Caldeira are not in it..
> I think this raises important questions about intra-scientific
> communication, but I don't think it means we need to worry about a 9 C
> sensitivity.
>
> In other words, just because you can't tell by looking at the clouds
> whether it is Tuesday does not make the day of the week unknown. It
> just means that information is not encoded very clearly in the clouds.
>
> One trouble with science is that stuff gets misused by non-target
> audiences. I see no reason to believe that Forest is actually worried
> about a nine degree sensitivity on the basis of this paper.
>
> As far as nonstatisticians are concerned, it pretty much looks like
> it's 3 C or a smidge under. Can we move on please?
>
> mt
Perhaps its a good time for me to ask about something I have been
wondering about.
Does this concept of "climate sensitivity" (currently estimated at 3 C
per doubling of CO2) have a tight definition?
I assume it is meant to apply no just to the doubling of CO2 but to
the doubling of CO2 equivalence of all greenhouse gases?
Seems to me (the non-expert) that it takes into account some feedbacks
but not all? I think it includes water vapor, correct? But is it
meant to include every feedback? Albedo, etc. ?
Seems that it could not include the feedback where heating releases
more greenhouse gases from the permafrost and other places since the
level of CO2 (or equivalent) is apparently already built into the
definition. On the other hand, if you are looking at data on the
history of the climate (history of temperature and greenhouse gas
levels), then that data would seem to include all the feedbacks. Is
there (or should there be) another definition of climate sensitivity
that includes all the feedbacks?
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